The present invention relates to a variable displacement compressor for use in, for example, compressing a refrigerant gas in a vehicle air conditioner or the like.
A variable displacement compressor of this type is described in, for example, Japanese Second (examined) Patent Publication No. 4-74549. The variable displacement compressor is provided with a suction chamber, a crank chamber and a discharge chamber and controls a displacement thereof depending on a pressure differential between the crank chamber and the suction chamber. For controlling the pressure differential between the crank chamber and the suction chamber, the compressor is provided with a particular passage which is for allowing the flow of gas from the crank chamber into the suction chamber and will be called hereinafter a bleed passage. The bleed passage, even being small, is always opened. Thus, the crank chamber and the suction chamber always communicate with each other.
If both chambers always communicate with each other, assuming that the compressor is stopped for hours and a temperature in a vehicle compartment is relatively high while a temperature around the compressor is relatively low, a phenomenon occurs that a large amount of liquid refrigerant in a low pressure side circuit flows into the crank chamber. If the compressor is started in this state, it is difficult for the liquid refrigerant to escape from the crank chamber so that the pressure differential between the crank chamber and the suction chamber is out of control to be increased. As a result, until the liquid refrigerant is removed from the crank chamber, the compressor continues to be operated with the minimum displacement so that the cooling power becomes insufficient.